In the field of positive displacement fluid apparatus, there exists a class or category generally referred to as scroll-type fluid apparatus which are characterized by the provision of wrap elements defining flank surfaces of generally spiroidal configuration about respective axes, which wrap elements lie in intermeshing, angularly offset relationship with their axes generally parallel such that relative orbital motion between the wrap elements results in the formation of one or more moving volumes between the wrap elements, defined by moving lines of coaction between the wrap elements at which their flank surfaces lie substantially tangent to each other. In a preferred form, the precise shape of the generally spiroidal flank surfaces comprise an involute of a circle, however, the term "generally spiroidal" is intended to encompass any form providing the requisite moving volumes during relative orbital motion between the wrap elements. Typically, end plate means are provided in sealing relationship to the wrap elements as they undergo relative orbital motion such that the moving volumes are effectively sealed. Reference may be had to U.S. Pat. No. 801,182 for an early disclosure of scroll-type fluid apparatus embodying this principle, or to U.S. Pat. No. 3,884,599 for a more recent disclosure.
It has been recognized that scroll-type fluid apparatus have utility in a wide variety of applications, including gas compressors or vacuum pumps for elevating the pressure of a gaseous working fluid; liquid pumps for transporting a liquid working fluid; or as an expansion engine for producing mechanical work by the expansion of a relatively high pressure gaseous working fluid. In the case of a gas compressor, the moving volumes defined between wrap elements originate at a radially outer portion thereof and progress inwardly while their volume is reduced, resulting in compression of the working gas which is then discharged at a radially inner portion of the wrap elements. Liquid pumps function in a similar fashion with the wrap elements configured such that no appreciable reduction in volume occurs as the volumes progress radially inwardly, while scroll-type expansion engines receive a relatively high pressure gaseous working fluid at the radially inner portion of their wrap elements, which then progresses radially outwardly in the moving volumes as they increase in volume, resulting in expansion of the working fluid and production of mechanical work.
In considering the kinematic relationship necessary in order to effect the requisite relative orbital motion between the wrap elements, it should be noted that at least three general approaches exist:
(1) maintaining one wrap element fixed while orbiting the other with respect thereto, i.e., causing it to undergo circular translation while maintaining a fixed angular relationship between the wrap elements; PA1 (2) orbiting both wrap elements in opposite directions while maintaining a fixed angular relationship therebetween; and PA1 (3) rotating both wrap elements about offset parallel axes while maintaining a fixed angular relationship therebetween.
A second consideration relevant to the relative orbital motion between wrap elements is the manner in which their flank surfaces are permitted to coact with each other; i.e., is actual contact permitted therebetween along the lines at which the surfaces lie substantially tangent, accompanied by a radial sealing force therebetween; or are constraints imposed thereon so as to maintain a slight clearance or gap therebetween. In this regard, it is convenient to term the former as "radially compliant" type, while the latter may be referred to as "fixed-crank" type. As used herein, the term "moving line coaction" is intended to be descriptive of both types, while the term "actual moving line contact" is limited to the radially compliant type. Reference may be had to U.S. Pat. No. 3,924,977 for disclosure of a radially compliant type drive mechanism, while U.S. Pat. No. 4,082,484 is illustrative of the fixed-crank type.
In many applications wherein gas compressors are utilized, it is desirable that the compressor be provided with variable capacity operation; particularly, in the field of refrigeration and air conditioning wherein gas compressors are utilized to compress a refrigerant gas such as Freon (a trademark of Du Pont), it is desirable that a particular refrigeration system be of variable capacity as to match the cooling or heating output of the system to the demand therefore at any particular time. To satisfy this need, many such systems today utilize centrifugal or reciprocating gas compressors provided with means for varying their capacity. It would, however, due to certain advantages associated with gas compressors of the scroll type, be desirable that this type compressor be provided with means for selectively varying its capacity so as to enable its application in the field of refrigeration and air conditioning, or in other applications where such variable capacity operation is required.